Fatigue life evaluation method of metallic components under random loads based on a new strain-life curve

Abstract

The fatigue life prediction methods of constant-amplitude load have been widely studied. However, a simple and mature random loads fatigue model is more worth exploring. In this paper, the battery box brackets were taken as the study case, the road simulation technology and statistical method are adopted to analyze the prediction accuracy of random loads which is based on ε-N curve and damage accumulation law, a fatigue damage calculation procedure of random loads was established. Firstly, both the road simulation and constant-amplitude experiments of bracket were conducted respectively on the hydraulic servo rig. Simultaneously, the strain loads were collected and the part ε-N curve was constructed. In accordance with the material and part ε-N curve, an improved double-parameter (u and v) Coffin-Manson model was proposed and a fatigue ε-N curve was plotted. Then the damage originated from machining process and geometrical uncertainty was corrected by u and v. Under random load conditions, u and v were calibrated furtherly by random load factor β. Finally, the damage of the brackets was recalculated and the result has a high precision. The double-parameter model coupled with β has strong adaptability to most fatigue uncertainties. A leaf spring experiment was also performed to verify the generality and validity of the model.